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Pain anatomy and physiology

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Pain anatomy and physiology

  1. 1. PAIN ANATOMY&PHYSIOLOGY Dr. M.ANEEQUE ALAM Anesthesia Resident Department of Anesthesiology Patel Hospital aneeque86@gmail.com
  2. 2. DEFINITION Pain is unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. Ref: International Association for the Study of Pain(IASP) o Pain is SUBJECTIVE phenomena
  3. 3. NOCICEPTION  Nocioception is a complex sequence of actions between tissue damage and the perception of pain.Its includes  Transduction  Transmission  Modulation  Perception
  4. 4.  Transduction: Translation of a (chemical) pain stimulus into electrical activity on nerve level.
  5. 5.  Transmission: Guidance of the pain – information through the nervous system, including: Ascending pathway  Primary afferent nerve-ends that go to the dorsal horn of the spinal cord.  ascending (inter-) neurons that project their information from the spinal cord to the brainstem and the hypothalamus/thalamus  The thalamic-cortical pathways
  6. 6.  Modulation: Modification of the nociceptive transmission through a number of humoral and neural effects  anti-nociceptive pathways (descending pathway)
  7. 7.  Perception: Observing the pain in a conscious way. Integration of transduction, transmission and modulation with the unique psychology of the individual, resulting in a subjective and emotional pain sensation
  8. 8. Opioids Local anesthetics Opioids
  9. 9. CLASSIFICATION PAIN IS CLASSIFIED INTO NOCICEPTIVE, NEUROPATHIC AND PSYCHOGENIC  1. Nociceptive is pain caused by tissue damage (inflammation) which stimulate pain receptors (nociceptors). 2. Neuropathic: (pain due to injury of nerve pathway) site of injury: Central Central pain (thalamic infarct). Mixed Plexus avulsion, Post herpetic neuralgia. Peripheral Neuroma, nerve compression, phantom, neuralgias. character: burning, tingling, numbness, pressing, squeezing, itching, constant +/- intermittent shooting, lancinating, electric. 3. Psychogenic: (difficult to differentiate whether secondary to or actual cause of pain), anxiety, depression (30% of depressives complain of pain on initial presentation).
  10. 10. Nociceptors are special receptors that respond only to noxious stimuli and generate nerve impulses which the brain interprets as “pain”  Free nerve endings oNon adaptive it’s a protective function to keep the individual trying to remove the damaging stimulus or to get away from it.
  11. 11. PRIMARY AFFERENT FIBERS Aδ – fast C – slow
  12. 12. CHARACTERISTICS A DELTA FIBRES C-FIBRES MYLENATION MYELINATED LARGE DIAMETER NON-MYLENATED SMALL DIAMETER CONDUCTION SPEED FAST(70-120 m/sec) SLOW(0.2-2 m/sec) ONSET FIRST FAST PAIN SECOND SLOW PAIN DURATION BRIEF LONG RECEPTIVE FIELD SMALL LARGE LOCALIZATION PRECISE DIFFUSE SENSORY QUALITY SHARP,PRICKING ACHING,DULL, BURNING CNS RESPONSE RELFEX,ANALYSIS EMOTIONAL, SUFFERING
  13. 13. TYPE OF PAIN FAST PAIN SLOW PAIN
  14. 14. FAST PAIN SLOW PAIN onset: during application of the stimulus Shortly after application if tissue damage occurs Duration: short duration Longer duration Nature: pricking Burning Afferent: A-delta fibers C-fibers Neurotransmitter: glutamate Substance-P Significance: * determine site & severity. * Initiate withdrawal reflexes. Associated with arousal, autonomic & emotional reactions Localization: well-localized Poorly-localized
  15. 15. THE NEUROCHEMICALS OF PAIN • Glutamate - Central • Substance P - Central • Brandykinin - Peripheral • Prostaglandins - Peripheral PAIN INITIATOR • Serotinin • Endorphins • Enkephalins • Dynorphin PAIN INHIBITOR
  16. 16. PAIN’S ASCENDING PATHWAY TO THE BRAIN THREE neurons from the receptor to the cerebral cortex  First order neuron:  Cell body located in the dorsal root ganglion.  Starts from free nerve ending  Ends at substantia gelatinosa
  17. 17.  Second order neuron:  Has cell body in the spinal cord or medulla oblongata • Starts from substantia gelatinosa  Axon decussate &  Terminate on 3rd order in thalamus neuron following Spinothalamic tract  Third order neuron:  Has cell body in thalamus  Axon terminates on cerebral cortex ipsilaterally
  18. 18. The Descending Pathway  pain afferents stimulates the neurons in periaqueductal gray (PAG) - gray matter surrounding the cerebral aqueduct in the midbrain results in activation of efferent anti-nociceptive pathways  from there the impulses are transmitted through the spinal cord to the dorsal horn  there thay inhibit or block transmission of nociceptive signals at the level of dorsal horn
  19. 19. GATE THEORY Melzack & Wall (1965) . non-painful input closes the "gates" to painful input
  20. 20. APPLICATIONS OF GATE THEORY Stimulation of touch fibres for pain relief:  TENS (transcutaneous electrical nerve stimulation)  Acupuncture  Massage
  21. 21. PAIN TOLERANCE  It is the maximum intensity of pain can be tolerated by the subject without obvious complaint.  Pain tolerance is affected by a number of factors: - Anxiety, depression & fatigue ------>  pain tolerance. - rest, sever exercise & strong emotional excitement ------>  pain tolerance.
  22. 22. Hyperalgesia Increased pain from a stimulus that normally provokes pain Allodynia Pain due to a stimulus that does not normally provoke pain.
  23. 23. PAIN FELT AWAY FROM THE ORIGINAL SITE OF THE PAINFUL STIMULUS.
  24. 24. PHANTOM LIMB o sensations are described as perceptions that an individual experiences relating to a limb or an organ that is not physically part of the body o brain contains neuromatrix of the body image –neurosignature like a hologram
  25. 25. QUESTIONS?

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